<div class="panel panel-primary">
  <div class="panel-heading">双向绑定</div>
  <div class="panel-body">
    <!--通过双向绑定的方式将值传递给子组件-->
    <app-font-re-size [(size)] = "FontSize"></app-font-re-size>
    <span [style.font-size.px] = "FontSize">字体缩放</span>
  </div>
</div>